Many types of document printers have been developed including home and office impact, laser, led and inkjet printers. Larger printers may be used for office workgroup applications or in industrial high speed printing applications. Similarly, many special purpose ink-jet printers have been developed such as dedicated envelope addressing printers including the ADDRESSRIGHT line of addressing printers and the DM SERIES of postage metering mailing machines (including the DM 500) available from Pitney Bowes Inc. of Stamford, Conn.
In a typical color inkjet page printer, the media is a sheet of 8.5×11 inch sheet of paper having a narrow range of acceptable thickness values such as about 0.003 to about 0.015 inch thickness. In such color inkjet page printers, the paper is typically registered downward on a registration plate and the paper thickness determines the distance to the print head. However, mailing machines including postage meters may be required to print on media in a wide range of thicknesses. For example, such mailing machines typically print on postcards and stuffed envelopes that may vary from approximately 0.005 to 0.625 inch or thicker material. Additionally, sealed envelopes may include captured air and thus may exhibit “puffiness” in that the air may shift in the envelope as the mailing machine handles the media.
In inkjet printing systems, there are several sources of printing error including ink dot placement error. The first type of dot placement error relates to the media distance from the print head. In order to maintain printing quality, it is important to control the distance from the print head nozzles to the media. When any given ink drop is fired from an inkjet nozzle, it takes a path that lies within a conical space having its apex at the nozzle and its base at the surface of the paper. Therefore, as the distance between the nozzle and the paper is increased, the diameter of the circular region at the base of the dot placement cone where the drop could actually land on the paper increases. When media thickness varies widely in a printing system having a static print head height, the system cannot use bottom registration and also maintain print quality. Accordingly, certain mailing machines including postage meter printers such as the DM 500 top register envelopes using a registration plate with a print head opening in order to control the distance from the print head to the media surface. For accurate ink-jet ink drop placement, the distance between the print head and the media is typically maintained at less than 0.020 inches. Moreover, typical mailing machine postage meter printers currently utilize water based inkjet inks. Solvent based and electromagnetic (such as approximately ultraviolet radiation (UV)) curable inks are sometimes used in larger or industrial printing applications. The various water based inkjet inks may include dye based or pigment based inks and may also include taggants such as red fluorescent taggants. However, UV inks are used in bottom registered printers in industrial applications. In such bottom registered UV ink printers, partial curing may be used in certain applications where it would not be possible in top registered printers.
In typical inkjet printers, there is a second source of dot placement error relating to nozzle to media distance. When the print head and the media are moved relative to one another in order to give the nozzle line access to all of the required areas on the paper, error based upon such movement is introduced. In a fixed head inkjet printer having a full printing width print head, only the media moves. In a shuttle head printer, at least the print head moves relative to the media and the media may also move relative to the print head. Since the time it takes for an ink drop to travel from the nozzle to the paper is dependent on the distance between the nozzle and the paper, variations in where the drop will land on the paper will occur with variations in the nozzle to paper distance.
When using several print heads, each with its own color, to produce a color print, the line of nozzles in each print head must be spaced some minimal distance from its neighbor that is governed by the width of the print heads. If the distance between the paper and the nozzles in a print head changes from that of the neighboring print heads, the placement of the different color dots will be different due to both types of dot placement error and thus will affect the resultant color image. Previously, top-registered mailing machine postage meter printers have generally utilized water based inkjet inks. Electromagnetic radiation curable (e.g., UV curable) inks have been used in certain other bottom registered printing systems including industrial sign printing applications.
Accordingly, there are several disadvantages of currently available printing systems and methods in general and of top-surface-registered printing systems in particular including the lack of suitable UV ink based top-registered printing systems.